This is a revised competing continuation of a grant focusing on the biomechanics of traumatic brain injury. In this continuation application, we study how tissue strains translate to cellular strains in the hippocampus, and proceed to concentrate on the NMDA receptor (NMDAR) mechanosensitivity and its role in hippocampal neuronal death. The broad, long term objective is to examine if regional neuronal populations are 'mechanically vulnerable'and susceptible to injury, to test if extrasynpatic and synpatic NMDARs have different mechanosensitivity, and to use the data on NMDAR mechanosensitivity to evaluate both immediate and delayed treatment strategies to reduce neuronal death after mechanical injury. The specific aims of this research plan are as follows: Aim 1: To describe the local micromechanical environment in organotypic hippocampal cultures subjected to realistic, in vivo deformations associated with injury. Aim 2: To measure the mechanoactivation threshold for extrasynaptic and synaptic NMDAR using recombinant NMDAR expressed in HEK293t cells and organotypic hippocampal cultures. Aim 3: To examine the activation and control of both JNK and ERK from mechanosensitive NMDARs, using this information to examine acute and delayed treatment strategies for reducing cell death after mechanical injury. Our overlying hypotheses are (a) at the same level of tissue stretch, neurons in the dentate gyrus and CAS experience higher mechanical deformations than other hippocampal regions, (b) NMDARs are stretch sensitive due to linkages to the cytoskeleton, (c) the mechanoactivation of extrasynaptic NMDA receptors will influence the activation of JNK through STEP, and (d) ERK activation will be preferentially controlled by synaptic NMDARs, with the duration of ERK signaling mediated by the activity of STEP. Relevance: This work will study how neurons in the hippocampus are injured during traumatic brain injury. The work will concentrate on studying the mechanical activation of a receptor known to play a role in memory formation and cell death. Using the information of receptor activation, the investigators will develop and test treatment strategies to reduce neuronal death following traumatic brain injury.